1. Field of the Invention
The present invention relates generally to athletic apparel, and in particular to athletic apparel for reducing the drag force on a wearer's appendage.
2. Description of Related Art
In many speed-based individual athletic events, such as bicycling, speed skating, and running, the difference between achieving first or second place is typically a fraction of a second. Individually-controllable factors, such as form and athletic power, are often the focus in the training for reducing performance time in such events. Drag due to the resistance of the movement of an athlete through a fluid such as the air or water is also a contributing factor in increasing performance time.
Any body moving through a fluid experiences a drag force, which may be divided into two components: frictional drag and pressure drag. Frictional drag is due to the friction between the fluid and the surfaces over which the fluid is flowing. The smoother the surface, the less frictional drag is generated by moving through the fluid.
Pressure or form drag derives from the eddying motions that are created by the motion of the body through the fluid, such as the formation of a region of separated flow or “wake” behind the body. The pressure in the wake is typically slightly less than the pressure in front of the body, and in extreme cases of cavitation, is significantly less than the pressure in front of the body. As such, to continue moving forward, the athlete must provide additional force to overcome the imbalance of the pressure forces in front of and behind the athlete.
The drag force on an athlete competing at lower speeds is generally dominated by the frictional component. It is known that improvements in performance times can be obtained by smoothing the surface of an athlete. For example, swimmers and bicyclists have long shaved the hair from legs, arm, and even heads in order to smooth the surface of the exposed skin. This shaving helps to reduce the friction between the athlete and the fluid (air or water) in which the athlete competes to save a fraction of second in performance time.
However, given that the shape of an athlete is not streamlined or optimized for motion through a fluid, the drag force on an athlete competing at high speeds is generally dominated by the pressure drag component. The pressure drag depends on factors such as the density of the fluid in which the athlete is moving, the projected frontal area of the athlete, and the velocity of the athlete. This drag component is generally inflexible, given that the size and operating power of the athlete as well as the density of the fluid in which the athlete operates remains fairly constant. An athlete may assume a crouching position in cycling or skiing to project a smaller frontal area to reduce pressure drag, but little can be done to streamline an athlete's form to reduce drag solely through training.
To decrease the influence of both frictional and pressure drag, athletic apparel and gear have been used to streamline the bodies of athletes. For example, aerodynamically streamlined helmets have been provided for cyclists.
However, with certain types of bluff bodies, such as spheres and cylinders, it has long been known that increasing surface roughness of the bluff body can actually reduce the pressure drag. For example, golf balls with dimples have significantly reduced drag and can travel much further than smooth surface golf balls. A sphere or cylinder with a roughened surface causes the laminar boundary layer to transition to a turbulent boundary layer at a lower velocity than that of a sphere or cylinder with a smooth surface. This turbulent boundary layer inhibits the separation of the fluid flowing around the body, causing the fluid to adhere to the surface contours of the body longer than the fluid would “stick” to a smooth body. As such, the cross-sectional area of the wake formed by the separation of the fluid flowing around the roughened body is smaller than the wake formed by the earlier separation of the same fluid flowing around a similarly-sized and shaped smooth body. For example, on a smooth sphere, using conventional notation with 0 degrees located at the leading edge of the sphere, the flow separation points are located at around 70 degrees and around 290 degrees on the sphere. On a roughened sphere, such as a golf ball with dimples, the turbulent boundary layer formed by the rough surface texture pushes the separation points toward 110 degrees and 250 degrees.
This technology has been applied to apparel worn by high-speed athletes. For example, speed skaters may attach so-called “Z strips” onto otherwise very smooth outfits to create a turbulent boundary layer. Further, U.S. Pat. No. 6,438,755 to MacDonald et al. provides an aerodynamic body suit, where each body segment of the suit is assigned a Reynolds number based upon the size and anticipated velocity of the body segment.
However, in some high speed athletic events, such as cycling, the rules of the sport prohibit the wearing of non-essential garments or garments for the purpose of reducing drag. As such, Z strips and body suits are not available to these athletes. Therefore, a need exists in the art for additional athletic garments with improved aerodynamic characteristics.